Method of controlling machine tool and machine tool

ABSTRACT

To provide a method of controlling a machine tool and a machine tool which allow preventing relieving interference without using a mechanism for causing an offset between a cutter ( 13 ) and a workpiece ( 50 ), a controller ( 40 ) performs control such that the workpiece ( 50 ) is machined by repeating the steps of: machining the workpiece ( 50 ) by moving the cutter ( 13 ) for machining the workpiece ( 50 ) in a direction parallel to a rotational axis of the cutter ( 50 ) while rotating the workpiece ( 50 ) together with the cutter ( 13 ); and returning the cutter ( 13 ) to a machining start position again after termination of the machining step, and performs offset control such that the cutter ( 13 ) is moved away from the workpiece ( 50 ) in a rotation direction of the cutter ( 13 ) upon the termination of the machining step.

TECHNICAL FIELD

The present invention relates to a method of controlling a machine tooland a machine tool.

BACKGROUND ART

A gear shaper is a machine tool including a cutter reciprocatingmechanism in which a working tool (hereinafter called cutter) isreciprocated in a center axis direction of an object to be machined(hereinafter called a workpiece) so as to machine the workpiece in itsadvancing path and to be moved away from the workpiece in its returningpath. Examples of such a gear shaper are disclosed in Patent Documents 1and 2 below.

FIG. 7 is a schematic view showing how a workpiece is machined in aconventional gear shaper.

As shown in FIG. 7, for example, the gear shaper as disclosed in PatentDocument 1 below performs gear cutting by shaping a workpiece 50 in sucha manner that a cutter 13 attached to a main spindle 12 is given arotational movement together with the workpiece 50 while beingreciprocated vertically (arrow L1 in FIG. 7), the workpiece 50 beingplaced on a table (not shown) on which the workpiece 50 is attached forthe machining.

The cutter 13 is in a vertical state near its rising end ([a] in FIG.7). The cutter 13 is moved straight downward in this state and machinesthe workpiece 50 during the downward movement ([a] to [c] in FIG. 7).Near its falling end, the cutter 13 is moved away (relieved) R from theworkpiece 50 in the arrow L2 direction by the amount of retraction (theamount of relieving) to become in a returning state ([d] in FIG. 7).

Next, the cutter 13 is moved upward in the state of [d]. Near its risingend, the cutter 13 approaches the workpiece 50 by the amount ofrelieving to become in the vertical state ([a] in FIG. 7). Then, thecutter 13 is moved downward again. By repeating these operations, thecutter 13 machines the workpiece 50 while being reciprocated vertically.

Here, the relieving direction of the cutter in relieving will bedescribed.

FIG. 8 is a schematic view showing the relieving direction of the cutterin relieving.

As shown in FIG. 8, cutting blades 13 a are formed in a side surface ofthe cutter 13. The tip of each cutting blade 13 a is located on anaddendum circle 13 b, and the root of each cutting blade 13 a is locatedon a dedendum circle 13 c.

FIG. 9 is a schematic view showing how an internal gear is formed by thecutter.

As shown in FIG. 9, teeth 50 a are formed in an inner surface of theworkpiece 50 by the cutter 13. Here, a portion indicated by a brokenline in the workpiece 50 is a portion 50 d to be chipped.

As shown in FIG. 8, the tip of each formed tooth 50 a is located on anaddendum circle 50 b, and the root of each tooth 50 a is located on adedendum circle 50 c. In relieving R, the cutter 13 is relieved R in adirection connecting the center O₂ of the cutter 13 and the center O₁ ofthe workpiece 50. In other words, a direction from the center O₂ of thecutter 13 toward the center O₁ of the workpiece 50 is a relievingdirection Rd.

However, in the conventional gear shaper described above, the cutter 13and the workpiece 50 during machining sometimes interfere with eachother (hereinafter called relieving interference) in the relieving R ofthe cutter 13, depending on the specifications of the workpiece to bemachined into an internal gear, the specifications of the cutter,machining conditions, and the like.

Here, the relieving interference will be described.

FIG. 10 is a schematic view showing how the relieving interferenceoccurs.

As shown in FIG. 10, the workpiece 50 during machining includes aportion 50 e chipped this time and a portion 50 f chipped in a previousrotation of the workpiece 50. For example, at a portion indicated by Iin FIG. 10, the cutter 13 in the relieving R as shown by a dashed-twodotted line in FIG. 10 sometimes interferes with the portion 50 fchipped in the previous rotation of the workpiece 50.

Note that, in FIG. 10, the relieving interference portion I is brieflyillustrated for the sake of understanding; however, the relievinginterference actually occurs at multiple positions in an extremely smallarea between the cutter 13 and the workpiece 50 in FIG. 10 due tomachining conditions such as the amount of cut, a cutting speed, and afeed speed. Moreover, if a rotation direction C2 of the cutter 13 and arotation direction C1 of the workpiece 50 during machining are as shownin the drawing, the interference does not occur in a lower half of thedrawing but occurs in an upper half thereof.

PRIOR ART DOCUMENT Patent Documents

Patent Document 1: JP-A Hei 10-109223

Patent Document 2: JP-A 2004-154921

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In order to prevent the relieving interference, the relieving directionRd shown in FIG. 10 needs to be changed to a direction of targetrelieving Rt with which the interference between the workpiece 50 andthe cutter 13 shown in FIG. 10 can be prevented. Thus, a method ofcausing a static offset in a relative position between the cutter 13 andthe workpiece 50 in a direction indicated by Y in FIG. 10 is known as amethod of changing the relieving direction Rd to the direction of thetarget relieving Rt.

FIG. 11 is a schematic view showing a conventional method of changingthe relieving direction Rd to the direction of the target relieving Rt.

As shown in Part (b) of FIG. 11, the center O₂ of the cutter 13 and thecenter O₁ of the workpiece 50 are shifted in the Y direction in FIG. 10while the relieving direction Rd shown in Part (a) of FIG. 11 is kept asit is. This causes the virtual center line of the machine tooloriginally directed in the relieving direction Rd to be directed in anO₂O₁ vector, and thus causes the relieving direction Rd to inclinerelative to the virtual center line. Thereby, the relieving direction Rdcan be changed to the direction of the target relieving Rt.

However, for the above conventional method of changing the relievingdirection Rd to the direction of the target relieving Rt, it isnecessary to add a mechanism capable of causing an offset between thecutter 13 and the workpiece 50 in the Y direction in FIG. 10 (see PatentDocument 1, for example). This causes problems of complicating a machineconfiguration and increasing cost.

Thus, an object of the present invention is to provide a method ofcontrolling a machine tool and a machine tool which allow preventingrelieving interference without using a mechanism for causing an offsetbetween a cutter and a workpiece.

Means for Solving the Problems

In a method of controlling a machine tool according to a first inventionto solve the above problems, the machine tool is configured to machine aworkpiece to be machined by repeating the steps of: machining theworkpiece by moving a cutter for machining the workpiece in a directionparallel to a rotational axis of the cutter while rotating the workpiecetogether with the cutter; and returning the cutter to a machining startposition again after termination of the machining step, the methodcharacterized in that

upon the termination of the machining step, offset control is performedsuch that the cutter is moved away from the workpiece in a rotationdirection of the cutter without change in a relative position of therotational axis of the cutter with respect to the workpiece.

A method of controlling a machine tool according to a second inventionto solve the above problems is the method of controlling a machine toolaccording to the first invention, characterized in that

upon the termination of the machining step, relieving is performed suchthat the cutter and the workpiece become away from each other bychanging relative positions of the rotational axis of the cutter and arotational axis of the workpiece with respect to each other, and,together with the relieving, the amount by which the cutter is movedaway from the workpiece in the rotation direction thereof by the offsetcontrol is adjusted, thereby controlling a direction of targetrelieving.

A method of controlling a machine tool according to a third invention tosolve the above problems is the method of controlling a machine toolaccording to the first invention, characterized in that

upon the termination of the machining step, relieving is performed suchthat the cutter is moved away from the workpiece, the amount of therelieving is adjusted, and the amount by which the cutter is moved awayfrom the workpiece in the rotation direction thereof by the offsetcontrol is adjusted, thereby controlling a direction and magnitude oftarget relieving.

A machine tool according to a fourth invention to solve the aboveproblems is a machine tool comprising:

workpiece rotation means for rotating a workpiece to be machined;

cutter rotation means for rotating a cutter for machining the workpiece;

cutter reciprocation means for moving the cutter in a direction parallelto a rotational axis of the cutter;

relieving means for moving the cutter away from the workpiece; and

control means for controlling the workpiece rotation means, the cutterrotation means, the cutter reciprocation means, and the relieving means,the machine tool characterized in that

the control means

-   -   performs control such that the workpiece is machined by        repeating the steps of: machining the workpiece by moving the        cutter for machining the workpiece in the direction parallel to        the rotational axis of the cutter while rotating the workpiece        together with the cutter; and returning the cutter to a        machining start position again after termination of the        machining step, and    -   performs offset control such that the cutter is moved away from        the workpiece in a rotation direction of the cutter upon the        termination of the machining step.

A machine tool according to a fifth invention to solve the aboveproblems is the machine tool according to the fourth invention,characterized in that

the control means

performs control such that relieving is performed in which the cutter ismoved away from the workpiece upon the termination of the machiningstep, and

adjusts the amount by which the cutter is moved away from the workpiecein the rotation direction thereof by the offset control together withthe relieving, thereby controlling a direction of target relieving.

A machine tool according to a sixth invention to solve the aboveproblems is the machine tool according to the fourth invention,characterized in that

the control means

-   -   performs control such that relieving is performed in which the        cutter is moved away from the workpiece upon the termination of        the machining step, and

adjusts the amount of the relieving and the amount by which the cutteris moved away from the workpiece in the rotation direction thereof bythe offset control, thereby controlling a direction and magnitude oftarget relieving.

Effects of the Invention

The present invention can provide a method of controlling a machine tooland a machine tool which allow preventing relieving interference withoutusing a mechanism for causing an offset between a cutter and aworkpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] FIG. 1 is a schematic view showing a method of preventingrelieving interference in a machine tool according to a first embodimentof the present invention.

[FIG. 2] FIG. 2 is a schematic view showing a method of controlling acutter in relieving according to the first embodiment of the presentinvention.

[FIG. 3] FIG. 3 is a schematic view showing a method of controlling acutter in relieving according to a second embodiment of the presentinvention.

[FIG. 4] FIG. 4 is a schematic view showing principal portions of themachine tool according to the first embodiment of the present invention.

[FIG. 5] FIG. 5 is a cross-sectional view showing the principal portionsof the machine tool according to the first embodiment of the presentinvention.

[FIG. 6] FIG. 6 is a schematic view showing a method of controlling themachine tool according to the first embodiment of the present inventionin machining a workpiece.

[FIG. 7] FIG. 7 is a schematic view showing how a workpiece is machinedin a conventional gear shaper.

[FIG. 8] FIG. 8 is a schematic view showing a relieving direction of acutter in relieving.

[FIG. 9] FIG. 9 is a schematic view showing how an internal gear isformed by the cutter.

[FIG. 10] FIG. 10 is a schematic view showing how relieving interferenceoccurs.

[FIG. 11] FIG. 11 is a schematic view showing a conventional method ofchanging a relieving direction Rd to a direction of target relieving Rt.

MODES FOR CARRYING OUT THE INVENTION

Hereinbelow, a method of controlling a machine tool and a machine toolaccording to embodiments of the present invention will be described withreference to the drawings.

Embodiment 1

First of all, description will be given of a structure of a machine toolaccording to a first embodiment of the present invention.

FIG. 4 is a schematic view showing principal portions of the machinetool according to the first embodiment of the present invention. FIG. 5is a cross-sectional view showing the principal portions of the machinetool according to the first embodiment of the present invention.

As shown in FIGS. 4 and 5, in the machine tool according to thisembodiment, a cutter head 10 is supported on a not-shown machine toolmain body through a support 11 to be movable in a horizontal directionin FIGS. 4 and 5.

A main spindle 12 is placed in the cutter head 10 to extend in avertical direction in FIGS. 4 and 5. A gear 14 is attached to the mainspindle 12. The main spindle 12 has such a structure as to be slidablein the gear 14 in the vertical direction and to be rotated in itsrotation direction together with the gear 14. The main spindle 12 isrotated with the rotation of the gear 14.

The gear 14 is driven by a main spindle driving motor 41 through a gear42. It is preferable to use a servomotor as the main spindle drivingmotor 41. The use of the servomotor as the main spindle driving motor 41allows control of a rotation angle of a cutter 13 with high speed andhigh accuracy. The cutter 13 is attached to a lower end portion of themain spindle 12, and is rotated in a C2 direction.

In a portion above the cutter head 10A, a crankshaft 19, a camshaft 25,and an eccentric shaft 29 are placed in the machine tool main body to berotatable about their respective shaft centers. A crank faceplateportion 20 is attached to the crankshaft 19. The crank faceplate portion20 is rotated about a center 20A of the crank faceplate portion 20 bythe rotation of the crankshaft 19.

A sliding portion 17 is placed on the crank faceplate portion 20 to bemovable on a surface of the crank faceplate portion 20 with a ball screw22. An end portion of a crank arm 15 is attached to the sliding portion17 through a pin 18. The crank arm 15 is swingable about the pin 18.

Further, the center 20A of the crank faceplate portion and the center ofthe pin 18 are attached to be eccentric to each other. The amount ofeccentricity between the center 20A of the crank faceplate portion 20and the center of the pin 18 can be adjusted by adjusting the ball screw22 to move the sliding portion 17 on the crank faceplate portion. Theamount of eccentricity between the center 20A of the crank faceplateportion and the center of the pin 18 is associated with the length ofthe vertical reciprocating movement of the main spindle 12, i.e., thelarger the amount of eccentricity, the longer the length of the verticalreciprocating movement of the main spindle 12. The other end portion ofthe crank arm 15 is attached to an upper end portion of the main spindle12 through a spherical bearing 16.

Further, a motor 35 for main spindle reciprocating movement is coupledto the crankshaft 19 through gears 23 and 24. It is preferable to use aservomotor as the motor 35 for main spindle reciprocating movement. Theuse of the servomotor as the motor 35 for main spindle reciprocatingmovement allows control of the crankshaft 19 with high speed and highaccuracy.

A camshaft driving motor 36 is coupled to the camshaft 25 through gears37 and 38. It is preferable to use a servomotor as the camshaft drivingmotor 36. The use of the servomotor as the camshaft driving motor 36allows control of a rotation angle of the camshaft 25 with high speedand high accuracy, and also allows control of the camshaft driving motor36 in synchronization with control of the motor 35 for main spindlereciprocating movement.

Further, a cam 26 is attached to the camshaft 25. The cam 26 is alsorotated with the rotation of the camshaft 25. The cam 26 is constitutedof two cams overlapping with each other or formed in one unit with theirphases (angles) shifted from each other. These two cams are normal camseach having a shape in which the radius of the cam changes in acircumferential direction thereof. The shape of the cam 26 causes theamount, by which the cutter 13 moves backward from or moves forward to aworkpiece, to be changed in accordance with the rotation angle of thecamshaft 25.

An eccentric shaft faceplate portion 33 is attached to the eccentricshaft 29, and is rotatable in a Y2 direction about a center 33A of theeccentric shaft faceplate portion 33 in conjunction with the movement ofthe eccentric shaft 29. An end portion of a relieving rod 30 is attachedto the eccentric shaft faceplate portion 33 through a pin 32 in such away that the center 33A and the center of the pin 32 are eccentric toeach other. The other end portion of the relieving rod 30 is attached toa left end portion of the cutter head 10 in the drawing through a pin 31in such a way that the cutter head 10 is movable in the horizontaldirection in FIGS. 4 and 5.

Further, a cam lever 28 is attached to the eccentric shaft faceplateportion 33 to be rotatable about the center 33A. Two cam followers 27are attached to the cam lever 28. The two cam followers 27 are incontact with the cam 26 to interpose the cam 26 between them. One of thecam followers 27 is in contact only with the outer circumference of oneof the two cams in the cam 26 having a shape constituted of these camsoverlapping with each other or formed in one unit. Meanwhile, the othercam follower 27 is in contact only with the outer circumference of theother cam.

When the cam 26 is rotated, a distance between the center of the cam 26and each cam follower 27 changes, so that the cam lever 28 is rotatedabout the center 33A in the Y2 direction. In conjunction with therotation of the cam lever 28, the eccentric shaft 29 and the eccentricshaft faceplate portion 33 are rotated about the center 33A in the Y2direction.

These are the structure of the machine tool according to the firstembodiment of the present invention.

Next, description will be given of an operation of the machine toolaccording to the first embodiment of the present invention.

A controller 40 performs numerical control on the main spindle drivingmotor 41, the motor 35 for main spindle reciprocating movement, and thecamshaft driving motor 36. The controller 40 issues a desiredsynchronous instruction, which is suited to a shape into which aworkpiece 50 is to be machined, to the main spindle driving motor 41,the motor 35 for main spindle reciprocating movement, and the camshaftdriving motor 36, and thereby performs synchronous control thereon withhigh speed and high accuracy.

When the motor 35 for main spindle reciprocating movement rotates in adirection, the crankshaft 19 coupled to the motor 35 for main spindlereciprocating movement is rotated in a direction. With the rotation ofthe crankshaft 19, the crank faceplate portion 20 and the slidingportion 17 are rotated about the crankshaft 19, so that the crank arm 15is vertically reciprocated. In conjunction with the vertical movement ofthe crank arm 15, the cutter 13 is vertically reciprocated in a Y1direction.

The length of the vertical reciprocating movement of the cutter 13 isdetermined by the amount of eccentricity between the center of thecrankshaft 19 and the center of the pin 18. In the changing of thelength of the vertical reciprocating movement of the main spindle 12,the ball screw 22 is adjusted to move the sliding portion 17 and tothereby adjust the amount of eccentricity between the center of thecrankshaft 19 and the center of the pin 18, so that the length of thevertical reciprocating movement can be changed.

In response to the given synchronous instruction issued by thecontroller 40 and suited to the shape into which the workpiece 50 is tobe machined, the camshaft driving motor 36 rotates in a desireddirection in synchronization with the rotation of the motor 35 for mainspindle reciprocating movement, and thereby rotates the camshaft 25 sothat the rotation angle of the camshaft 25 may reach a desired angle.With the rotation of the camshaft driving motor 36, the camshaft 25coupled to the camshaft driving motor 36 is rotated. In conjunction withthe rotation of the camshaft 25, the cam lever 28 and the eccentricshaft faceplate portion 33 are rotated about the center 33A in the Y2direction.

In conjunction with the rotational movement of the eccentric shaftfaceplate portion 33, the relieving rod 30 is reciprocated in a Y3direction. In conjunction with the reciprocating movement of therelieving rod 30, the cutter head 10 is moved in the horizontaldirection in FIGS. 4 and 5. In conjunction with the movement of thecutter head 10 in the horizontal direction in FIGS. 4 and 5, the cutter13 can move forward to or move backward from the workpiece 50. In thisway, the machine tool according to this embodiment can be operated asdesired by the controller 40.

These are the operation of the machine tool according to the firstembodiment of the present invention.

Next, description will be given of the method of controlling the machinetool according to the first embodiment of the present invention inmachining a workpiece.

FIG. 6 is a schematic view showing the method of controlling the machinetool according to the first embodiment of the present invention inmachining a workpiece.

As shown in FIG. 6, the controller 40 performs control such that thecutter 13 may be moved in the order of [A]→[B]→[C] in a machining step,and moved in the order of [C]→[D]→[E]→[F]→[A] in a return step.

In the machining step, the cutter 13 starts the machining of theworkpiece 50 at a position indicated by [A] in FIG. 6. A positionindicated by [B] in FIG. 6 indicates a position of the cutter 13 duringthe machining of the workpiece 50. Then, the cutter 13 terminates themachining of the workpiece 50 at a position indicated by [C] in FIG. 6.

In the return step, the cutter 13 starts relieving R at the positionindicated by [C] in FIG. 6. In other words, the cutter 13 starts therelieving R upon the termination of the machining of the workpiece 50.

According to this embodiment, the relieving interference is prevented bycontrolling the amount of rotation of the cutter 13 in the rotationdirection C2, i.e., by performing control such that the cutter 13 may bemoved away from the workpiece 50 in the rotation direction C2(hereinafter referred to as offset control). Such control is performedby use of a specific phenomenon where, as shown in the relievinginterference occurrence portion I (see FIG. 10), the relievinginterference occurs in an extremely small area located in an upper halfof the cutter 13 and the workpiece 50 in FIG. 10 but does not occur in alower half thereof, in accordance with the rotation direction C2 of thecutter 13 and a rotation direction C1 of the workpiece 50 in machining.

Here, description will be given of a method of preventing relievinginterference in the machine tool according to the first embodiment ofthe present invention.

FIG. 1 is a schematic view showing a method of preventing relievinginterference in the machine tool according to the first embodiment ofthe present invention.

As shown in FIG. 1, the controller 40 performs, in synchronization withthe relieving R, offset control such that relieving Rr in the rotationdirection of the cutter 13 as shown in FIG. 1 may be performed inaddition to the normal rotational movement of the cutter 13, and therebysubstantially realizes target relieving Rt.

In other words, a machine tool capable of causing the controller 40 toperform numerical control on the rotation angle of the cutter 13, suchas the machine tool according to this embodiment, can direct a directionof the target relieving Rt for a cutting blade 13 a of the cutter 13 inthe relieving interference portion I to a desired direction byperforming offset control such that rotation by the amount correspondingto the relieving Rr in the rotation direction C2 of the cutter 13 may beadditionally imposed on a position of the cutter 13 during the normalrotational movement in its rotation direction.

For example, suppose a case where the specifications of the workpieceare a module of 10, a pressure angle of 25°, the number of internalteeth of 46, a torsion direction of teeth being spur (straight cutgear), and a cut depth of 17.8 mm, where the specifications of thecutter are the number of blades of 15 and an outer diameter of 169.2 mm,and where machining conditions are a circumferential feed of 0.278mm/stroke and a radial feed of 0.015 mm/stroke. In this case, in orderto prevent the relieving interference in the relieving interferenceportion I as illustrated in FIG. 1, offset control is performed suchthat the cutter 13 may be moved away from the workpiece 50 in itsrotation direction C2 by 0.3 mm (note that, this is a length on thecircumference of a circle (PCD) connecting intermediate portions betweenthe tips and the roots of the cutting blades 13 a of the cutter 13 toeach other, and is 0.23° when converted into the rotation angle).

Here, the stroke means one reciprocating movement of the cutter 13, andindicates a path that the cutter 13 travels once along top deadcenter→[A]→[B]→[C]→bottom dead center→[D]→[E]→[F]→top dead center inFIG. 6.

Note that, in FIG. 1, the relieving interference portion I is brieflyillustrated for the sake of understanding; however, the relievinginterference actually occurs at multiple positions in the extremelysmall area located in the upper half of the cutter 13 and the workpiece50 in FIG. 1 in accordance with the rotation direction C2 of the cutter13 and the rotation direction C1 of the workpiece 50 in machining.Hence, the amount by which rotation is to be additionally imposed by theoffset control on one occurrence position can be different from that onanother occurrence position.

FIG. 2 is a schematic view showing a method of controlling the cutter inrelieving according to the first embodiment of the present invention.

As shown in FIG. 2, even if the relieving R is of fixed length, themachine tool according to this embodiment is capable of controlling adirection of the target relieving Rt by adjusting the amount ofrelieving Rr in the rotation direction of the cutter 13 by the offsetcontrol.

In other words, even if the relieving R is of fixed length, control canbe performed such that the target relieving Rt may be set to targetrelieving Rt′ by setting the relieving Rr in the rotation direction ofthe cutter 13 to relieving Rr′ in the rotation direction by the offsetcontrol.

These are the method of preventing the relieving interference in themachine tool according to the first embodiment of the present invention.

As shown in FIG. 6, the controller 40 terminates the relieving R at aposition indicated by [D] in FIG. 6. The controller 40 controls therelieving Rr in the rotation direction of the cutter 13 at the positionsindicated by [C] and [D] in FIG. 6. A position indicated by [E] in FIG.6 indicates a position of the cutter 13 during returning. Note that, inFIG. 6, the amount of relieving is exaggeratingly shown for the sake ofunderstanding.

The cutter 13 makes an approach to the workpiece 50 (i.e., which isopposite to the relieving) at a position indicated by [F] in FIG. 6. Thecontroller 40 cancels the offset control at the positions indicated by[F] and [A] in FIG. 6 to return the position of the cutter 13 in therotation direction C2 to the normal position thereof in the rotationmovement. Then, the cutter 13 starts the machining of the workpiece 50at the position indicated by [A] in FIG. 6.

These are the method of controlling the machine tool in the machining ofthe workpiece according to the first embodiment of the presentinvention.

Thus, although the conventional gear shaper has to control the targetrelieving Rt by causing an offset between the cutter 13 and theworkpiece 50 in the Y direction in FIG. 10, the machine tool accordingto this embodiment is capable of controlling the target relieving Rt forthe cutting blade 13 a of the cutter 13 in the relieving interferenceportion I only by the control of the rotation angle of the cutter 13.

Accordingly, a conventionally required mechanism to cause an offsetbetween the cutter 13 and the workpiece 50 in the Y direction in FIG. 10is no longer required. This simplifies a machine configuration andreduces cost.

Moreover, the method of preventing the relieving interference in themachine tool according to this embodiment can be implemented only bychanging a program for the controller 40, which in turn reduces cost.

Embodiment 2

Hereinbelow, description will be given of a method of controlling amachine tool in relieving according to a second embodiment of thepresent invention. Note that, the configuration of the machine toolaccording to this embodiment is the same as that of the firstembodiment.

FIG. 3 is a schematic view showing the method of controlling a cutter inrelieving according to the second embodiment of the present invention.

As shown in FIG. 3, a machine tool capable of performing numericalcontrol on the rotation angle of the cutter 13 and the amount ofrelieving of the cutter 13 in a relieving direction Rd, such as themachine tool according to this embodiment, can control a direction andmagnitude (i.e., vector) of the target relieving Rt by adjusting theamount of relieving R in the relieving direction Rd and the amount ofrelieving Rr in the rotation direction of the cutter 13 by the offsetcontrol.

In other words, control can be performed such that the target relievingRt may be set to target relieving Rt″ by setting the relieving R in therelieving direction Rd to relieving R′ and setting the relieving Rr inthe rotation direction of the cutter 13 by the offset control to therelieving Rr′ in the rotation direction. Hence, an optimum vector of thetarget relieving Rt″ can be achieved.

These are the method of controlling the machine tool in relievingaccording to the second embodiment of the present invention.

As has been described, with the method of controlling the machine toolaccording to the present invention, in the machine tool configured tomachine the workpiece 50 to be machined by repeating the steps of:machining the workpiece 50 by moving the cutter 13 for machining theworkpiece 50 in the vertical direction while rotating the workpiece 50together with the cutter 13; and returning the cutter 13 to itsmachining start position again after termination of this machining step,offset control is performed such that the cutter 13 may be moved awayfrom the workpiece 50 in its rotation direction upon the termination ofthe machining step. Thereby, the method is capable of controlling thetarget relieving Rt for the cutting blade 13 a of the cutter 13 in therelieving interference portion I only by the control of the rotationangle of the cutter 13.

Accordingly, a conventionally required mechanism to cause an offsetbetween the cutter 13 and the workpiece 50 in the Y direction in FIG. 10is no longer required. This simplifies a machine configuration andreduces cost.

Moreover, the method of preventing the relieving interference in themachine tool according to this embodiment can be implemented only bychanging a program for the controller 40, which in turn reduces cost.

Further, upon the termination of the machining step, the relieving R isperformed such that the cutter 13 may be moved away from the workpiece50, and the amount by which the cutter 13 is moved away from theworkpiece 50 in its rotation direction by the offset control is adjustedtogether with the relieving R. Thereby, control can be performed suchthat the target relieving Rt may be set to the target relieving Rt′ evenif the relieving R is of fixed length.

Further, upon the termination of the machining step, the relieving R′ isperformed such that the cutter 13 may be moved away from the workpiece50, and the amount by which the cutter 13 is moved away from theworkpiece 50 in its rotation direction by the offset control is adjustedtogether with the adjusting of the amount of the relieving R′. Thereby,an optimum direction and magnitude of the target relieving Rt″ can beachieved.

Furthermore, the machine tool according to the present inventionincludes workpiece rotation means for rotating the workpiece 50 to bemachined; cutter rotation means for rotating the cutter 13 for machiningthe workpiece 50; cutter vertical movement means for moving the cutter13 in the vertical direction; relieving means for moving the cutter 13away from the workpiece 50; and the controller 40 for controlling theworkpiece rotation means, the cutter rotation means, the cutter verticalmovement means, and the relieving means. In the machine tool, thecontroller 40 performs control such that the workpiece 50 is machined byrepeating the steps of: machining the workpiece 50 by moving the cutter50 for machining the workpiece 50 in the vertical direction whilerotating the workpiece 50 together with the cutter 13; and returning thecutter 13 to a machining start position again after termination of themachining step, and performs offset control such that the cutter 13 ismoved away from the workpiece 50 in its rotation direction upon thetermination of the machining step. Thereby, the machine tool is capableof controlling the target relieving Rt for the cutting blade 13 a of thecutter 13 in the relieving interference portion I only by the control ofthe rotation angle of the cutter 13.

Accordingly, a conventionally required mechanism to cause an offsetbetween the cutter 13 and the workpiece 50 in the Y direction in FIG. 10is no longer required. This simplifies a machine configuration andreduces cost.

Moreover, the method of preventing the relieving interference in themachine tool according to this embodiment can be implemented only bychanging a program for the controller 40, which in turn reduces cost.

Further, upon the termination of the machining step, the controller 40performs control such that the relieving R may be performed in which thecutter 13 is moved away from the workpiece 50, and, together with therelieving R, adjusts the amount by which the cutter 13 is moved awayfrom the workpiece 50 in its rotation direction by the offset control.Thereby, control can be performed such that the target relieving Rt maybe set to the target relieving Rt′ even if the relieving R is of fixedlength.

Further, upon the termination of the machining step, the controller 40performs control such that the relieving R′ may be performed in whichthe cutter 13 is moved away from the workpiece 50, adjusts the amount ofthis relieving R′, and adjusts the amount by which the cutter 13 ismoved away from the workpiece 50 in its rotation direction by the offsetcontrol. Thereby, an optimum direction and magnitude of the targetrelieving Rt″ can be achieved.

Therefore, the present invention can provide the method of controlling amachine tool and a machine tool which allow preventing relievinginterference without using a mechanism for causing an offset between thecutter 13 and the workpiece 50.

INDUSTRIAL APPLICABILITY

The present invention can be used for a method of controlling a machinetool and a machine tool, particularly for a method of controlling amachine tool configured to machine a workpiece into an internal gear andfor a machine tool.

EXPLANATION OF REFERENCE NUMERALS

-   10 cutter head-   11 support-   12 main spindle-   13 cutter-   14 gear-   15 crank arm-   16 spherical bearing-   17 sliding portion-   18 pin-   19 crankshaft-   20 crank faceplate portion-   22 ball screw-   23, 24 gear-   25 camshaft-   26 cam-   27 cam follower-   28 cam lever-   29 eccentric shaft-   30 relieving rod-   31, 32 pin-   33 eccentric shaft faceplate portion-   35 motor for main spindle reciprocating movement-   36 camshaft driving motor-   37, 38 gear-   40 controller-   41 main spindle driving motor-   42 gear-   50 work

1. A method of controlling a machine tool configured to machine aworkpiece to be machined by repeating the steps of: machining theworkpiece by moving a cutter for machining the workpiece in a directionparallel to a rotational axis of the cutter while rotating the workpiecetogether with the cutter; and returning the cutter to a machining startposition again after termination of the machining step, the methodcharacterized in that upon the termination of the machining step, offsetcontrol is performed such that the cutter is moved away from theworkpiece in a rotation direction of the cutter without change in arelative position of the rotational axis of the cutter with respect tothe workpiece.
 2. The method of controlling a machine tool according toclaim 1, characterized in that upon the termination of the machiningstep, relieving is performed such that the cutter and the workpiecebecome away from each other by changing relative positions of therotational axis of the cutter and a rotational axis of the workpiecewith respect to each other, and, together with the relieving, the amountby which the cutter is moved away from the workpiece in the rotationdirection thereof by the offset control is adjusted, thereby controllinga direction of target relieving.
 3. The method of controlling a machinetool according to claim 1, characterized in that upon the termination ofthe machining step, relieving is performed such that the cutter is movedaway from the workpiece, the amount of the relieving is adjusted, andthe amount by which the cutter is moved away from the workpiece in therotation direction thereof by the offset control is adjusted, therebycontrolling a direction and magnitude of target relieving.
 4. A machinetool comprising: workpiece rotation means for rotating a workpiece to bemachined; cutter rotation means for rotating a cutter for machining theworkpiece; cutter reciprocation means for moving the cutter in adirection parallel to a rotational axis of the cutter; relieving meansfor moving the cutter away from the workpiece; and control means forcontrolling the workpiece rotation means, the cutter rotation means, thecutter reciprocation means, and the relieving means, the machine toolcharacterized in that the control means performs control such that theworkpiece is machined by repeating the steps of: machining the workpieceby moving the cutter for machining the workpiece in the directionparallel to the rotational axis of the cutter while rotating theworkpiece together with the cutter; and returning the cutter to amachining start position again after termination of the machining step,and performs offset control such that the cutter is moved away from theworkpiece in a rotation direction of the cutter upon the termination ofthe machining step.
 5. The machine tool according to claim 4,characterized in that the control means performs control such thatrelieving is performed in which the cutter is moved away from theworkpiece upon the termination of the machining step, and adjusts theamount by which the cutter is moved away from the workpiece in therotation direction thereof by the offset control together with therelieving, thereby controlling a direction of target relieving.
 6. Themachine tool according to claim 4, characterized in that the controlmeans performs control such that relieving is performed in which thecutter is moved away from the workpiece upon the termination of themachining step, and adjusts the amount of the relieving and the amountby which the cutter is moved away from the workpiece in the rotationdirection thereof by the offset control, thereby controlling a directionand magnitude of target relieving.